The chemical structure of Dutasteride is the following:

Dutasteride is a selective inhibitor of the type 1 and type 2 isoforms of steroid 5α-reductase (5 AR), an intracellular enzyme that converts testosterone to 5α-dihydrotestosterone (DHT). Dutasteride is currently available in the market as Avodart, Avidart, Avolve, Duagen, Dutas, Dutagen, Duprost, etc. as a drug for benign prostatic hyperplasia, and is used for the treatment of prostate diseases such as prostate cancer, acne, male pattern baldness, hirsutism, and prostate gland enlargement.
The first reported synthetic methods for Dutasteride were described in WO 95/07927 and U.S. Pat. No. 5,565,467.
U.S. Pat. No. 5,565,467 shows two different ways to get Dutasteride, one of them includes dehydrogenation of 17β-N-[2,5-bis(trifluoromethyl)phenyl]carbamoyl-4-aza-5-α-androstane-3-one in the presence of catalysts 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and bis(trimethylsilyl) trifluoroacetamide in dioxane as solvent. This process involves several steps.
The second option is more simple and starts from 4-aza-5α-androst-1-ene-3-one-17β-carboxylic acid. This second way to produce Dutasteride is similar to that disclosed in WO 95/07927.
It is important to note that, in both patents, the carboxylic group in 4-aza-5α-androst-1-ene-3-one-17β-carboxylic acid (II) (See Scheme 1) is transformed first into the corresponding acyl halide by thionyl chloride and after that it is transformed into the corresponding amide group. Both patents employ the same basic reagents but different conditions (See Table I). Only the patent WO 9507927 (1995) discloses a yield of 48%.

TABLE IDocument U.S. Pat.Reagents toDocument WO 9507927 -No. 5,565,467 -produce:Example 2Example 2Acyl halideThionyl chlorideThionyl chlorideTolueneDMFPyridinePyridineTime reaction2 hs2.5-3 hsAmide group2,5-bis(trifluoro-2,5-bis(trifluoro-methyl)phenylaminemethyl)phenylamine4-dimethylamino pyridineTime reaction15-16 hs4-6 hsGlobal yield48%Not disclosedtwo steps
Afterwards, a modification of the same process (WO 9507927) in a large scale (18 kg) was disclosed in WO 02/46207 with a yield of 37-57%.
Other different process was disclosed in WO 2004/007523. This process has more steps and seems to be too complicated to be performed in industrial scale.
On the other hand, no information related to polymorphic forms is given in the mentioned patents. Only the U.S. Pat. No. 5,565,467 patent makes reference that many organic compounds can exist in more than one crystalline form, but no specific information related to Dutasteride is presented.
The polymorphic forms of Dutasteride are disclosed in US 2004/077673A1, where two crystalline and one amorphous forms are described. The crystalline forms are named I and II and they are characterized by their X-ray powder diffraction pattern and infrared spectra.